/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    public:
        TreeNode* pruneTree(TreeNode* root) {
            if(root == nullptr) return nullptr;
            root->left = pruneTree(root->left);
            root->right = pruneTree(root->right);
            if(root->left ==nullptr && root->right == nullptr && root->val == 0){
                //delete root;
                root = nullptr;
            }
            return root;
        }
    };